1. Field of the Invention
The present invention relates to system and method for polishing a float glass, and more particularly to system and method for polishing a float glass used for liquid crystal displays.
2. Description of the Related Art
Generally, it is very important that a glass (or, a glass pane) used for liquid crystal displays keeps its flatness to a certain level so as to accurately realize images of the liquid crystal display. Thus, fine waviness or unevenness existing on a surface of a float glass formed in a float manner should be removed.
Such a glass polishing process may be classified into so-called ‘Oscar’ type polishing in which glasses are individually polished one by one, and so-called ‘inline’ type polishing in which a series of glasses are successively polished. Also, the glass polishing process may be classified into ‘single side polishing’ in which only one surface of a glass is polished, and ‘double side polishing’ in which both surfaces of a glass are polished.
In a conventional glass polishing device, while a polishing plate (or, an upper plate) having a polishing pad installed thereto is moved in a horizontal direction and a polishing stage (or, a lower plate or a glass setting plate) having a glass located thereon is rotated, the glass is polished using a slurry freely falling down onto the polishing plate.
In recent, the size of a float glass is gradually increased to cope with the trend of enlargement of liquid crystal displays, and accordingly the sizes of an upper plate of the polishing plate and a lower plate of the polishing stage are increased. In this circumstance, in a conventional glass polishing device, linear velocities at various radii of the upper plate driven in contact with the float glass are different from each other, which causes a difference in the degree of polishing in a radial direction of the upper plate and results in making it difficult to keep overall polishing evenness of the float glass. In particularly, in case of a device for polishing a float glass with a larger size, since a moving range of the upper plate of the polishing plate is restricted, it is relatively difficult to keep evenness of polishing at edge portions (for example, about 20 to 30 cm) of a rectangular float glass to be polished. In addition, if the moving range of the polishing plate is set greater so as to polish edge portions of a float glass, it is hard to keep balance in a radial direction of the polishing plate, and other portions than corner portions of the float glass may be unnecessarily over-polished.
Meanwhile, a conventional glass polishing device applies a force to a float glass by means of self weight of the upper plate, or the polishing plate, so it is impossible to apply uniform force to the float glass over the entire area of the polishing plate. In this reason, evenness at every region of a float glass finally polished is not regular, which results in more frequent defects in the float glass. In particular, as the size of the polishing plate is increased (up to about 1,000 mm in diameter) due to the enlargement of liquid crystal displays, this problem becomes more serious. In other words, in the conventional art, the entire portion of the polishing plate contacted with a float glass does not press the float glass with the same force, but the force applied to the float glass is gradually decreased outwards from the center of the polishing plate, thereby making it difficult to ensure uniformity of the polishing process.